The technical field of the invention is that of electrical contactors, especially those used in electric motors comprising batteries and serving to propel motor vehicles or spacecraft such as satellites.
The present invention relates more especially to a pyrotechnically operated electrical contactor making it possible, in the event of an anomaly, to open the electrical circuit upstream of the defective battery element and to close a shunt circuit, so as to isolate the defective battery element while still ensuring continuity of the electrical circuit. This type of contactor is used to prevent an electric motor from automatically breaking down in the event of a malfunction of one of its battery elements.
Several kinds of pyrotechnically operated electrical contactors have already formed the subject of patents.
A first type of contactor is described in U.S. Pat. No. 3,885,223. This is a pyrotechnically operated electrical contactor provided in one of its chambers with a tube having a flattened cross section. As long as this contactor has not yet operated, it closes a circuit by means of the external surface of the casing of the tube, at the two points on the flattened closed cross section which are furthest apart. In the operating phase, the combustion gases enter the tube and generate a pressure such that the tube deforms and assumes a circular cross section.
Thus, in the direction in which the tube was radially contracted, the initial electrical contacts were broken and, on the other hand, in the direction in which it was radially expanded, two new, diametrically opposed, electrical contacts were established.
The electrical contactor described in European Patent EP 0,665,566 is also pyrotechnically operated. It employs a gas generator whose function is to move a conducting piece in contact with another conducting piece so as to separate them in order to interrupt the electric current.
Electrical contactors that can be used in the field of application of electric motors provided with batteries, and that have the dual function of opening an electrical circuit and of closing another one almost simultaneously, must have two characteristics sought after by those skilled in the art: they must, on the one hand, act in an extremely short time and, on the other hand, they must be non-dissipative, that is to say the resistance of the active circuit, and particularly the resistance of the contacts, must be reduced to the minimum in order to avoid, as far as possible, energy dissipation by the Joule effect, whereas the resistance of the unactivated circuit is infinite.
The contactor according to the invention meets this dual requirement.
The subject of the present invention relates to an electrical contactor, especially for a battery, having of a hollow body defining an upstream part in which a pyrotechnic initiation device is located and a downstream part in which a piston is housed, characterized in that:
axe2x80x94the downstream part has at least three electrical contact points;
bxe2x80x94the piston, having a conducting part initially connecting the first electrical contact point to the second electrical contact point, can move due to the effect of the pressure generated by the gases arising from the combustion of the pyrotechnic initiation device in order to connect at least one other electrical contact point.
According to a preferred embodiment of the invention, the downstream part has three electrical contact points and the piston, whose conducting part connects the first electrical contact point to the second electrical contact point, can move due to the effect of the pressure generated by the gases arising from the combustion of the pyrotechnic initiation device in order to connect the second electrical contact point to the third electrical contact point. Preferably, apart from its conducting part, the piston is made entirely from an insulating solid material.
Advantageously, the hollow body is an elongate tube. Preferably, the electrical contact points are located in the side wall of the downstream part of the tube.
Advantageously, the electrical contact points comprise a plurality of conducting studs. Preferably, the three studs are fixed, aligned and uniformly spaced and the piston undergoes a translational movement in the downstream part when it is subjected to the pressure of the combustion gases arising from the pyrotechnic initiation device.
Advantageously, the conducting part of the piston includes of a plate which remains constantly in contact with at least two studs during its movement and which, at a given instant during the said movement, is momentarily connected to the three studs.
Thus, the opening of the first circuit takes place while the electric current is already flowing in the second circuit, making it possible to avoid, for a short time, the simultaneous opening of the two electrical circuits.
This is because momentarily interrupting the electric current could cause undesirable spurious phenomena to occur such as, for example, the functional members supplied being inopportunely reset to zero.
Preferably, the downstream part of the tube has a conical free end allowing the piston set into motion by the combustion gases to terminate its travel by being jammed in the said conical end. In this way, the piston remains fixed in this position without any risk of it returning to the downstream part.
Advantageously, the pyrotechnic initiation device is screwed into the upstream part of the elongate tube.
Preferably, each conducting stud is inserted into an insulating structure fitted into the wall of the downstream part of the tube.
Preferably, each conducting stud is inserted into an insulating hollow screw which is screwed into the wall of the downstream part of the elongate tube.
Advantageously, each stud and the plate are made of a copper-based material.
According to a preferred embodiment of the invention, the hollow body is made of an aluminium-based light alloy.
Preferably, the pyrotechnic initiation device is constructed from a hot-wire initiator of the type of those used in motor-vehicle mass production. Advantageously, the pyrotechnic charge of the said initiator consists of an oxidation-reduction ignition composition.
The contactor according to the invention has the advantage of being lightweight, simple in design and small in size.
The pieces involved in the operation of the mechanism of the contactor are subjected to moderate frictional forces. Thus, their movement requires only a small amount of pyrotechnic material in the initiator and their mechanical strength may be provided by making them from a light material.
In addition, when the contactor is in the switching phase, it ensures at all times that electric current is flowing in one or other of the two electrical circuits, thus avoiding a complete and momentary cut-off which could result in undesirable spurious phenomena with unpredictable consequences for the circuit.
Finally, another advantage afforded by the invention is the non-dissipative character of the contactor, resulting in there being no energy dissipation by the Joule effect.